|
-
POSTING RULES

-
Donate yearly (please).
-
Advertise in here!
-
Today's Posts
|
Insert Pics
|

09-22-2010, 04:34 PM
|
|
|
|
Join Date: Feb 2005
Location: Minneapolis
Posts: 2,473
|
|
Quote:
Originally Posted by sprucemoose
I remember this, as I was right there when it happened (I was leading him back to parking on my scooter.) The details are a bit fuzzy, but I'm almost certain that there was a hard landing or other incident that occurred immediately prior to the nose gear failing during the taxi on the grass. I would be careful about using this as a data point in the discussion without having the full story.
|
Was that perchance a brilliantly colored Orange/Yellow RV? Just curious....
|

09-22-2010, 05:41 PM
|
|
|
|
Join Date: Oct 2005
Location: Savannah, GA
Posts: 1,849
|
|
I can tell you they did it right with the RV-10 nose gear. If I had a smaller -A would look to puttting a bigger fork and tire up there. Less chance to dig in.
My question for all the -As that went over what was the CG location and overall weight? If you are nose heavy, carrying a little extra speed, have the flaps down and not pulling full back on the elevator you are setting yourself up for a bad situation. But sometimes you can being doing everything right and just hit a hole.
__________________
Todd
N110TD
RV-10 Vesta V8 LS2/BMA EFIS/One formerly flying at 3J1 Hobbs stopped at 150 hours
Savannah, GA and Ridgeland, SC
|

09-22-2010, 06:00 PM
|
 |
|
|
Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 10,011
|
|
But the extra weight...
Quote:
Originally Posted by RVbySDI
.....
The link provides some discussion of the possibility of creating more bending forces after the mod. Given this, Bob's mod may not necessarily solve the problem.
|
...will certainly change the resonant frequency of the system, and that seems tied into the overall problem.
__________________
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
|

09-22-2010, 06:52 PM
|
 |
|
|
Join Date: Jan 2006
Location: Tucson, AZ
Posts: 818
|
|
Is there really a simple fix?
I have been following this thread for some time. I too am building a RV-7A and am weeks away from completion. No kidding I really am almost ready for final assembly and inspection.
Warning: This maybe a long winded post.
The nose gear issues have been concerning me since seeing the nose over video in England some years ago. It has made me question if I made the right decision building the "A".
I have in my possession the bent nose gear leg from the RV-9A builder that nosed over in So. California. I performed a hardness test on it to verify that it was properly heat treated (it was). It is a constant reminder of the issues concerning the nose gear sensitivity.
I am Mechanical Engineer (design) in the defense industry and have been involved in several extensive testing of our "No doubt, work the first time products-our products only have to work once or people die." but the most dynamic testing I have ever witnessed was when I was interning at Grumman Aerospace Corp. It tests of the F-14 landing gear during simulated carrier landings. It was done in a lab and was frightening to watch. I have never seen metal bend and twist under such dynamic loading since that test. It left a imprint in my mind just how dynamic the landing event is and how complex the analysis is to properly design a gear system to survive in that environment. If you compare the F-15 to the F-14 you will see that the f-14 is about 10,000 lbs heavier then the F-15. They are roughly the same size, have two massive engines and fly really fast and carry (or carried) lots of bombs and missiles. The main reason the F-14 is that much heavier is to survive the carrier landing and takeoffs.
Now to the main point of my post.
Van made certain compromises when coming up with the "A" model. He had to morph an existing design (RV-6) without making major structural changes. This may have played a huge role in the nose gear design choice that was made.
I have seen some builders who have implemented some of their own changes to the design thinking they are making a real improvement. However the failure mode of the gear leg is complex. An example is the builder who changed the fork and increased the wheel diameter. The thought was it increased the height of the nut above the ground. However his changed also increase the yoke length which increase the moment (torque) on the gear leg. Unfortunately after all that work his RV flipped. His attempt to improve the design may have actually increased the chance that it would fail.
I work with a lot of smart engineers with all the right analysis tools but unless you can demonstrate through testing, first by actually failing a nose gear of the current design and then test the new improvements under the same conditions, it is unlikely you can prove that a fix really fixes the problem.
We believe that if we can get the nut higher off the ground then we don't have a problem, right? But what happens when the gear bends (nut hasn't hit the ground yet) and the wheel pant hits the gear leg and then the tire hits the wheel pant and the tire stops spinning dramatically increasing the torque on the gear leg, causing it bend more, then the nut hits the ground.
My point is that it needs to be looked at as a system. It is not just the wheel size, yoke, gear leg it is all of these.
It would be nice to believe any improvement would help but unless we truly understand the event (aircraft loading, speeds, surface conditions, etc) and actually fail a gear (capture the event on close-up video) we won't truly understand how to fix it and if the fix would really work.
A (properly loaded) nose gear, yoke, wheel installed on a simulated engine engine mount nose gear socket mounted on a test rig towed behind a pickup truck on a grass/field (with gopher holes) at 50-60 mph wouldn't be to far out of the question as a test bed. You don't have to go Mach 1 to test the concepts out.
I am sure a Aerospace and Mechanical Engineering Department at a University might be interested in offering it up as a senior project for their students. Back in the day I would have jumped at the chance on working on this as a senior project. So one option might be to pool some money, and offer it to a University to take on the challenge.
I have some University contacts here at the U of A, but maybe a University closer to Van's might be more appropriate.
Food for thought, your mileage may vary.
__________________
Dream it, Build it, Fly it
Paul Merems (EAA Tech Counselor, EAA Sheetmetal Workshop Instructor/Volunteer 12 yrs)
ExperimentalAero- HANGAR BANNERS
www.experimentalaero.com
RV-7A (Flying since 2010)/RV-4 (sold 1990)
Tucson, Arizona 85749
Last edited by DeltaRomeo : 09-22-2010 at 07:00 PM.
Reason: typo fix (curtain to certain)
|

09-22-2010, 07:06 PM
|
 |
|
|
Join Date: Sep 2005
Location: Maple Grove, MN
Posts: 2,334
|
|
Bump this as it is very pertinent to a couple other threads currently raging...
__________________
Alex Peterson
RV6A N66AP 1700+ hours
KADC, Wadena, MN
|

09-22-2010, 07:19 PM
|
 |
|
|
Join Date: Jan 2005
Location: Marion IA
Posts: 1,095
|
|
Quote:
Originally Posted by FresnoR
So just for arguments' sake, what would it take to get the RV-10 nose gear assembly on a 7 or 9?
|
Rick, thanks for posting the excellent and relevent picture.
What is striking to me is that the -10 nosegear seems to allow some vertical motion without significant deformation of the spring steel. I imagine that if one were to push upwards on the wheel from the bottom, the rubber donuts would compress pretty far before the steel began to bend significantly. Because of the length of the gear leg, a small compression at the donut must equal a large movement at the wheel.
I wonder how much suspension travel happens with "mostly" the dounts compressing... even 2-3" would be great. As the rubber compresses and releases its energy, it isn't going to flip the plane over. It is a much more "lossy" spring (aka damper) than the steel gear leg.
Very nice design. I'd be willing to change out my mount and gear for that design. I know it would likely weigh more, but the nosegear weight limitation would likely be different (or non existant). The weight & balance shift that would occur might be able to be offset by moving the engine back a fraction of an inch.
__________________
Dave Gribble VAF #232
Building RV-9A N149DG (slider, IO-320, IFR)
Restored and Flying Beech Super III N3698Q
Marion IA
Struggling with fiberglass
There is no sport equal to that which aviators enjoy while being carried through the air on great white wings." Wilbur Wright, 1905
|

09-22-2010, 08:21 PM
|
|
|
|
Join Date: Mar 2007
Location: West Texas
Posts: 282
|
|
Cleveland?
Alex,
In response to your original question, I have a similar setup. My 1996 nosegear includes a Cleveland wheel and the setup is different than later kits.
Below are two pictures comparing a 7A nosewheel set up with a 6A on the right. The 6A also came with the big nose fork which I have replaced with the one on the left.
Dave A.
6A build
Last edited by koda2 : 09-22-2010 at 08:23 PM.
Reason: signature added & text
|

09-22-2010, 09:33 PM
|
|
|
|
Join Date: Nov 2008
Location: Scio,Oregon
Posts: 261
|
|
NG diameters
I was just measuring the NG for an idea I have for a bolt on damper/stopper to limit the aft movement of the NG.
The failure occurrs when the gear is deflected aft to a point it can't recover and gives way. The whole nut thing is when the failure is imminent. Just imagine the angle that would have to be present to have the nut contact earth.
I measured the diameter at the lower bend(1.010 dia.). 8" up the leg (.910 dia.) and at the socket it tapers up to 1.125". The leg is actually reduced in diameter .100" right where they appear to fail. That seems and actually looks pretty dramatic. Just slide your and up and down the leg and you can feel the thin area.
If the gear leg was just an even taper from the lower bend up to the socket that would be a pretty substantial strength improvement. Any engineering thoughts about this? I know it would remove some spring from the leg.
****, right now they are designed to fail if you ask me. I know, I know, keep the stick in your gut.
|

09-22-2010, 09:48 PM
|
|
|
|
Join Date: Aug 2009
Location: Chicago/Tucson
Posts: 73
|
|
Well here goes:
I would contribute to do a study as Pmerems suggests. We must establish whether there is a problem and what the failure mode is, all the rest of the conversation here is speculation.
If, and it is a big if, there is ample evidence that there is a problem, then it will be in Van's court to improve the design. Van's will be compelled by their additional liability in this matter if a study bears out a design problem.
We as builders and fliers of Van's aircraft cannot redesign the gear in this forum, we can fund a study.
__________________
Jordan Kaplan
RV-7A
Just starting the journey
QB Fuse and Wings in the shop
Last edited by jlk : 09-22-2010 at 09:51 PM.
|

09-22-2010, 10:39 PM
|
|
|
|
Join Date: May 2007
Location: salem Oregon
Posts: 1,023
|
|
I saw a oleo strut on a 6A recently. Time will tell gentleman. When I hear more I'll let you know. Hope to find out more in the weeks to come.
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
All times are GMT -6. The time now is 06:51 AM.
|